In the application of lasers in dentistry, there is a delicate balance between the benefits gained from laser treatment and the heat-related damage arising from laser irradiation. Hence, it is necessary to understand the different processes associated with the irradiation of lasers on dental materials. To obtain insight for the development of a safe and general-purpose laser for dentistry, the present study examines the physical effects associated with the irradiation of a near-infrared free-electron laser (FEL) on the surface of a commonly used silver dental alloy. The irradiation experiments using a 2900-nm FEL confirmed the formation of a pit in the dental alloy. The pit was formed with one macro-pulse of FEL irradiation, therefore, suggesting the possibility of efficient material processing with an FEL. Additionally, there was only a slight increase in the silver alloy temperature (less than 0.9 °C) despite the long duration of FEL irradiation, thus inferring that fixed prostheses in the oral cavity can be processed by FEL without thermal damage to the surrounding tissue. These results indicate that dental hard tissues and dental materials in the oral cavity can be safely and efficiently processed by the irradiation of a laser, which has the high repetition rate of a femtosecond laser pulse with a wavelength around 2900 nm.

Previously, we indicated that a silver staining method generally used in protein gel electrophoresis could be applied to stain undecalcified tooth sections for observation of fine structures in dentin and cementum. In this study, we attempted to observe the carious lesions of enamel and dentin with the silver staining method. When undecalcified ground sections of teeth were stained with the staining method, carious lesions on dentin showed layer staining pattern, and the staining patterns seemed to be corresponding to the histological zone of the carious lesions. Furthermore, it was clear that discoloration of tooth sections stained by silver was promoted by UV light exposure, as a result, the enamel carious lesions could be observed. Our results suggested an application possibility of the silver staining to detect the carious lesions in both dentin and enamel.